[llvm] [Support] Compile out unused dominator DFS sorting (PR #202832)

[Alexis Engelke via llvm-commits]

aengelke wrote:

This has no effect on stage2 builds, neither in code size nor in performance: https://llvm-compile-time-tracker.com/compare.php?from=fb2d6709f289525497cdf731bf32085401c6b962&to=f273c2716e09c2225c1ea577c5dad725b08e7ab9&stat=instructions:u

I don't think this is worth it, this specialization should be done (and apparently is) in a (Thin)LTO build.

https://github.com/llvm/llvm-project/pull/202832